Adding guns to the equation just adds more weapons available to both attackers and victims.

Victims don't carry around weapons to defend themselves right now, if they were able to get hold of a gun that wouldn't change. Essentially the only thing that changes is on the attacker's side; great, so now you've added guns to that equation.

Well, if you do that, then I guess you also need to arm the police. Most police force in the UK is not firearmed (the UK has a strong notion that the police are civilians in uniform), but if you're giving more tools to attackers, the police will need to respond in kind.

So effectively, by adding guns, you've done nothing to prevent acid attacks and you made it so that the police making a mistake can end a life.

Edit: I misinterpreted the parent comment!